Mapping marine oil spillage using eddy current flaw detection techniques
Jack Stalnaker, University of Louisiana at Lafayette
Controlled source electromagnetic methods have long been used to detect defects in sensitive metallic components. Electromagnetic induction is particularly attractive because it is rapid, inexpensive, and easily employed by laymen and technicians. This so-called eddy current flaw detection assumes that a perfect, known current configuration will be induced in a metallic target. Deviations from the expected current density are detected and in its simplest incarnation, the detection device sounds an alarm. The source is harmonic, and penetration depth is tunable as a function of frequency.
An oil spill presents a curiously similar scenario. A conductor (the sea water) should support a predictable induced current density. The presence of oil will alter the current patterns from normalcy, providing a means of detection. Furthermore, the character and amount of deviancy can be tied to spill thickness. As eddy current flaw detection is commonly used to detect fractures in metal with no surface expression, induction could detect submerged or emulsified oil at depths selected by transmitter frequency.
Most oil spill detection and mapping technologies are rudimentary, and based on visual identification of sheen. Detection in this manner is subject to the attentiveness of the observer, and may be affected by sunlight, weather, and non-oil floating masses. Aside from various rules of thumb, thickness is not measured, and submerged oil is missed altogether. The proposed technique can be used with extant airborne exploration electromagnetic geophysical technology, and does not require heavy modeling or inversion. Modeling can however be used to investigate the affects of spill shape and size on induced current patterns. In fact, preliminary three dimensional finite element modeling has shown a detectable change in current patterns with changes in spill thickness.
Jack Stalnaker is an assistant professor in the Geology Department at University of Louisiana at Lafayette. His areas of research include near surface geophysics, controlled-source electromagnetic geophysics, statistical signal processing, physics-based modeling, archaeology, computer science, and environmental studies. Jack received a Ph.D. in geophysics from Texas A\&M University in 2004, and Bachelor’s degrees in geology and in anthropology from College of Charleston in 1998. Before coming to Lafayette, Jack was a postdoctoral researcher in the Electrical Engineering Department at Northeastern University.